In 1926, an American man was born in Connecticut who would eventually captivate the international medical community for more than half a century and have a legacy that has left a significant mark on today’s understanding of modern neuroscience and human memory. Referred to inconspicuously as simply “H.M.,” Henry Molaison lived a normal life for most of his childhood. However, at age 10 he was involved in a bike accident and the resulting head trauma led to the development of epilepsy. In the years after the incident H.M. was plagued by daily seizures and severe pain, and as a result he was unable to lead a normal life. Desperate to find relief he visited neurosurgeon Dr. William Scoville. Dr. Scoville performed a radical brain surgery involving the bilateral removal of H.M.’s amygdala and hippocampus. After his surgery, H.M. developed anterograde amnesia, and his inability to form new memories was often cited by those who argued that he was no better off now than before the surgery. While most of the research conducted in regards to H.M. dealt with his pronounced anteretrograde amnesia, his episodes of retrograde amnesia also helped to expand the scientific community’s knowledge and understanding of the hippocampus and amygdala’s role in memory formation and recall (Godwin, n.d.).
Overview and Symptoms
Retrograde amnesia is a memory disorder characterized by the inability to recall memories of events dating prior to the onset of the disability. Unlike most neurological conditions, retrograde amnesia does not have a typical line of treatment, such as medications or therapies, that can change outcomes. There are four main types of retrograde amnesia that each express their symptoms in slightly different ways: pure retrograde amnesia, focal retrograde amnesia, isolated retrograde amnesia, and temporally graded retrograde amnesia. Pure retrograde amnesia is the only type of retrograde amnesia that is not accompanied by anteretrograde amnesia. In all other varieties of the disorder, patients are not only unable to recall memories prior to an accident, but also lose the ability to form new memories. (Winocur, Mcdonald, & Moscovitch, 2000). Focal retrograde amnesia is the only type without a noticeable physical disability along with memory problems. Isolated retrograde amnesia is similar to the other forms, but differs in that it is primarily the result of a lesion in the thalamus, and recalling memories is often even more difficult than in the other types of the disorder (Miller et al., 2001). In the case of temporally graded retrograde amnesia, patients are typically fortunate enough to recover most of the memories they lost after the incident which resulted in their condition (Acharya, n.d.). While all four of these types of retrograde amnesia affect patients differently, every type of retrograde amnesia can be simply defined as a type of amnesia that affects autobiographical memory primarily and semantic memory, (to a lesser degree), and leaves an individual unable to recall memories prior to the onset of amnesia. The primary symptom of retrograde amnesia is usually only memory loss, but physical issues that vary from patient to patient are quite common as well. Confusion and inability to recognize familiar faces are indicative symptoms of an amnesiac having memory loss.
In most cases, retrograde amnesia is brought about by damage to the hippocampus in the temporal lobe. There are, however, much wider reasons for the initiation of such damage in retrograde amnesia. The most common occurrence that results in hippocampal damage is head trauma. Some frequent events that result in head trauma include sports injuries, car accidents, and falling. As a result of head trauma, individuals may often (afterwards) have (what is known as) a coup countrecoup injury. In this type of injury, both sides of the brain are damaged - the side that absorbed the initial impact (coup), and the side opposite of the impact (countrecoup) (“Types of Neurologic Damage.,” n.d.). Another cause is anoxia and ischemic strokes. Epilepsy can also cause retrograde amnesia in addition to Korsakoff’s syndrome. Psychologically disturbing events, infectious conditions, surgery, psychiatric treatment, traumatic injuries, and damage to the temporal lobes and diencephalon can contribute to the onset of retrograde amnesia as well. While the hippocampus is not the primary area that is usually damaged in retrograde amnesia, damage may still occur here that can result in the disorder. Therapeutic measures such as electroconvulsive therapy (ECT) that may be used to treat conditions such as major depression can lead to short term memory loss, and in some cases clinically induce retrograde amnesia due to the effects of the treatment on the brain.
The most common method used to diagnose patients with retrograde amnesia, and any form of amnesia, is evaluating a patient’s factual knowledge abilities. Specifically, autobiographical memory is more important in testing whether or not a patient may be suffering from retrograde amnesia. To evaluate this, a physician or doctor may interview an individual to gain some insight into the capacity of their memory and their abilities. In an interview, a doctor will assess three areas of a patient’s life - childhood, early adulthood, and recent facts. Additionally, the neuroimaging techniques CT and MRI may be employed to assist in the diagnostic process, and abrupt decreases in brain activity in an EEG can indicate structural damage, a key sign of retrograde amnesia (Acharya, n.d.).
Typically, amnesia is the result of primary damage to a part in the brain, usually the hippocampus, which results in memory loss. In the case of retrograde amnesia, however, the hippocampus remains in tact for the most part, and other areas of the brain are affected that play important roles in declarative memory. In the case of retrograde amnesia, the main areas affected that result in severe memory loss experienced are the diencephalon and temporal lobes, specifically the thalamus, especially in isolated retrograde amnesia.
The course of treatment for a patient with retrograde amnesia depends considerably on which variety they have as well as the cause which initiated the disorder. A common path of treatment involves the use of a learning technique called classical conditioning, also known as Pavlovian learning, in which a stimulus can be used to evoke a response from a patient that can be used to gain back parts of lost autobiographical memory. As retrograde amnesia is closely associated with Korsakoff’s syndrome, injection of thiamine supplements into veins can also lessen the recovery time. Drugs may also be taken to mitigate tissue damage of brain structures. Some of the most common classes involved in pharmaceutical treatment include antiepileptic drugs and diuretics. If a doctor believes that a viral infection might have been involved in the induction of the disorder, then anticonvulsants, antibiotics, and steroids may be taken as well. If the amnesia was thought to be caused by psychological trauma, then hypnotherapy might be employed (Acharya, n.d.).
Henry Molaison - American memory patient who suffered from severe anteretrograde amnesia with episodes of retrograde amnesia simultaneously; more commonly referred to as “H.M.”
Amygdala - Almond shaped brain part in limbic system involved in fear and emotional memory
Hippocampus - Seahorse shaped brain part in limbic system involved in control of memory and emotion
Anteretrograde amnesia - Inability of the brain to form new memories after the onset of amnesia
Thalamus- Egg shaped brain part that relays sensory information to the cerebral cortex
Head trauma - Injury that causes brain trauma
Coup countrecoup injury - Injury that causes damage to both sides of the brain
Anoxia - Absence of oxygen
Korsakoff’s Syndrome - Disease associated with alcohol misuse that results in an individual fabricating false memories to cover up forgotten ones of past experiences
Electroconvulsive Therapy (ECT) - Method of reducing seizures by passing small electrical currents through the brain
Autobiographical Memory - Memories of personal experiences from an individual’s life
CT - Imaging technique that uses X-rays to take photos of organs and other body parts
MRI- Imaging technique that uses magnetic fields to take photos of organs and other body parts
EEG - Method used in electrophysiology to detect abnormal electrical activity in the brain
Declarative Memory - Memories of facts and events that can be consciously recalled; also known as explicit memory
Diencephalon- The posterior portion of the forebrain (prosencephalon) comprised of the thalamus, hypothalamus, pineal gland, and third ventricle
Classical Conditioning - Type of learning in which in which neutral and potent stimuli are paired together to generate a response
Diuretics - Drug class that promotes urine production
Hypnotherapy- Technique used in psychotherapy to elicit subconscious change by hypnosis
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